Negan is a casual, jolly, savage man who adores violence and mayhem. He is very intelligent and logical, possessing a knack for controlling and manipulating others. He has a strong affinity for profane language and offensive comments and a morbid, perverse sense of humor, seeming to enjoy the shock value. His charismatic persona and domineering presence allows him to easily intimidate friends and foes alike.

Perhaps stemming from his years as a school coach, he has a pedantic nature to him, reveling in helping others explore their thoughts, feelings, and ideas. He displays profound moments of wisdom when counseling people, keenly perceptive of abstractions that others may have missed.
In spite of his violent and savage nature, Negan can be very reasonable for the sake of practicality, like when he spared Carl's life to keep relations steady with Rick, even though Carl slaughtered many of the Saviors.

Negan does possess a sense of sympathy underneath his cold exterior, and even a sense of honor that leads him to be repulsed by certain acts against the weak, such as . He believes that his horrific methods of keeping his people in line, which involve burning the faces of rule breakers and using fear to keep people subjected, are to justify a greater good, and he does stick by his own code of ethics.
He adamantly believes in a philosophy that the strong are to protect the defenseless. For instance, he murders a Savior after he tries to rape Holly, claiming that if his men are to commit rape, then their goal of rebuilding civilization can never be achieved.

He also yells at Dwight for daring to beat a "defenseless child" and is even seen losing his temper at another leader who allows rape to ensue within their ranks, declaring them less than human, apparently unaware of the hypocrisy. Despite his odd sense of sympathy, he admits he has trouble feeling emotions properly due to losing someone close to him in the past.

Pre-Apocalypse
Virginia

Very little is known regarding Negan's early life other than he presumably grew up as a sports enthusiast. In adulthood, he became a High School Gym coach where he practiced a range of sports including billiards and ping-pong. He also worked as a used-car salesman, presumably as a part time occupation.
At some point, Negan was married to his wife, Lucille where they presumably lived together as an average married couple. Negan constantly strived to gain the admiration of his fellow peers where he occasionally invited several of his fellow students to play ping-pong against him inside his own personal garage, however he frequently belittled and humiliated his pupils through the use of his expressive and aggressive language which resulted in him receiving several complaints from the students' parents.

Post-Apocalypse

At some point after the outbreak, Negan established "The Saviors" and fiercely ruled over his men. Negan, along with his team (which includes at least 50 or more other men), had made a deal with the Hilltop Colony; they would use the weaponry that the other group was lacking to kill all zombies wandering near their premises, and in return, they would obtain half of Hilltop's supplies; such as livestock and crops. To get his point across, if a potential problem would arise, Negan and his men would resort to cruel and manic measures.

If they sense they are being tracked or if they feel they aren't getting a sufficient enough amount of supplies, they beat or kill the people from Hilltop. The group also sends "messages" to the community, which are usually very deadly, such as Gregory being stabbed by Ethan.
Later, Negan, along with fifty other Saviors, snuck up on Rick's group and subdued Rick by surprise. They lined up all of the survivors from the van (Rick Grimes, Carl Grimes, Glenn, Maggie Greene, Sophia, Michonne, and Heath), telling them that he wanted revenge for the Saviors that were killed.

Without an agreement from Rick, Negan made a deal; everything that belonged to the Alexandria Safe-Zone, now belonged to the Saviors. He introduced his weapon of choice: Lucille, a baseball bat covered in barbed wire.
After a long talk about the new world order and whom he should beat to death using Lucille. He finally chose his victim at random: Glenn. Maggie panicked, as Glenn attempted talking Negan out of it. Negan ignored him and smashed Glenn's skull in by slamming Lucille down hard on Glenn's head. Negan laughed and when Glenn attempted to get to his feet, the former remarked that "he's taking it like a champ" before swinging Lucille at Glenn, dislocating his jaw and beating Glenn to death.

Negan told the group that the Saviors would be back in one week to collect half of everything they have, or there would be more killings. Rick vowed that he would avenge Glenn and kill Negan. He laughed at this, beating Rick with his bare hands in response, before leaving with his Saviors.

-Comes hopping by in a bunny suit with an orange tabby cat sidekick in his basket--hands the man a basket full of Cadbury eggs, chocolates, plastic eggs full of goodies and a stuffed rabbit-"Happy Easter!"-Hops away to his next victim-